Hayden sent his specimen to Joseph Leidy, who identified it as half of a tail vertebra and tentatively assigned it to the European dinosaur genus Poekilopleuron as Poicilopleuron [sic] valens.

[6] O. C. Marsh and Edward Drinker Cope, who were in scientific competition with each other, went on to coin several other genera based on similarly sparse material that would later figure in the taxonomy of Allosaurus.

[18] Although sporadic work at what became known as the Cleveland-Lloyd Dinosaur Quarry in Emery County, Utah, had taken place as early as 1927 and the fossil site itself described by William L. Stokes in 1945,[19] major operations did not begin there until 1960.

Such studies have covered topics including skeletal variation,[23] growth,[24][25] skull construction,[26] hunting methods,[27] the brain,[28] and the possibility of gregarious living and parental care.

In 2005, Oliver Rauhut and Regina Fechner describe the right maxilla of a juvenile theropod (IPFUB Gui Th 4) from the Guimarota mine, that was stored in the collections of the Institute of Geological Sciences of the Free University of Berlin.

[47] In 2010, new Allosaurus elements from the Andrés quarry are reported, including new cranial remains such as a right quadrate-quadratojudal, two lacrimals, a right dentary, a right frontal, the posterior end of the right mandible and a complete braincase.

[48] The remains were collected between 1988 and 2010, and include cranial elements (such as the maxilla, nasal, lacrimals, prefrontal, postorbitals, frontals, palatines, quadrate, quadratojugal, squamosal, vomer, braincase, articular, surangulars, prearticular, angulars, supradentary and coronoid, isolated mesial and lateral teeth) and postcranial elements (intercentrum of the atlas, dorsal, sacral and caudal vertebrae, cervical and dorsal ribs, chevrons, coracoid, ilium, pubes, femora, tibiae, fibulae, astragalus and calcaneum, distal tarsal III, second, tird, and fourth metatarsals, and several phalanges).

[48] Duplicate elements reported in the thesis include the previously mentioned left ilium, a fragmentary pubic peduncle in articulation with the pubes, and a right frontal, caudal vertebra, and pedal phalanges of a third much smaller individual.

[6] It is known from the remains of at least 60 individuals, all found in the Kimmeridgian–Tithonian Upper Jurassic-age Morrison Formation of the United States, spread across Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, and Wyoming.

The first specimen to wear the identification was unearthed in Dinosaur National Monument in northeastern Utah, with the original "Big Al" individual subsequently recognized as belonging to the same species.

[37] A. fragilis, A. jimmadseni, A. anax, A. amplus, and A. lucasi are all known from remains discovered in the Kimmeridgian–Tithonian Upper Jurassic-age Morrison Formation of the United States, spread across Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah and Wyoming.

The specific name comes from the Ancient Greek ἄναξ (anax, "king", "lord" or "tribal chief"), and is intended to be an updated reference to the now dubious saurischian genus Saurophaganax, to which the fossils were previously attributed.

[48] The Vale Frades Allosaurus, consisting of a partial skull and cervical vertebrae and ribs, is the type specimen of A. europaeus,[45] although the validity of that species has been previously questioned.

[53] In his 1988 book, Predatory Dinosaurs of the World, the freelance artist & author Gregory S. Paul proposed that A. fragilis had tall pointed horns and a slender build compared to a postulated second species A. atrox, as well as not being a different sex due to rarity.

A. medius was named by Marsh in 1888 for various specimens from the Early Cretaceous Arundel Formation of Maryland,[73] although most of the remains were removed by Richard Swann Lull to the new ornithopod species Dryosaurus grandis, except for a tooth.

[53] Labrosaurus stechowi, described in 1920 by Janensch based on isolated Ceratosaurus-like teeth from the Tendaguru beds of Tanzania,[88] was listed by Donald F. Glut as a species of Allosaurus,[85] is now considered a dubious ceratosaurian related to Ceratosaurus.

[81] An astragalus (ankle bone) thought to belong to a species of Allosaurus was found at Cape Paterson, Victoria in Early Cretaceous beds in southeastern Australia.

[105] John Foster, a specialist on the Morrison Formation, suggests that 1 t (1.1 short tons) is reasonable for large adults of A. fragilis, but that 700 kg (1,500 lb) is a closer estimate for individuals represented by the average-sized thigh bones he has measured.

[93] A more recent discovery is a partial skeleton from the Peterson Quarry in Morrison rocks of New Mexico; this large allosaurid was suggested to be a potential specimen of Saurophaganax prior to this taxon's 2024 reassessment.

However, it has been noted that these scales are more similar to those of sauropods, and due to the presence of non-theropod remains associated with the tail of "Big Al Two" there is a possibility that this skin impression is not from Allosaurus.

[53] Allosauridae has at times been proposed as ancestral to the Tyrannosauridae (which would make it paraphyletic), one example being Gregory S. Paul's Predatory Dinosaurs of the World,[129] but this has been rejected, with tyrannosaurids identified as members of a separate branch of theropods, the Coelurosauria.

[26] Their interpretations were challenged by other researchers, who found no modern analogs to a hatchet attack and considered it more likely that the skull was strong to compensate for its open construction when absorbing the stresses from struggling prey.

[139] The original authors noted that Allosaurus itself has no modern equivalent, that the tooth row is well-suited to such an attack, and that articulations in the skull cited by their detractors as problematic actually helped protect the palate and lessen stress.

[141][142] A biomechanical study published in 2013 by Eric Snively and colleagues found that Allosaurus had an unusually low attachment point on the skull for the longissimus capitis superficialis neck muscle compared to other theropods such as Tyrannosaurus.

[152][108] A single dead adult Barosaurus or Brachiosaurus would have had enough calories to sustain multiple large theropods for weeks or months,[153] though the vast majority of the Morrison's sauropod fossil record consisted of much smaller-bodied taxa such as Camarasaurus lentus or Diplodocus.

[156] The fact that allosaurs were more likely to survive and heal even when severe fractures limited their locomotion abilities can be explained, in part, by different resource accessibility paradigms for the two groups, as allosauroids generally lived in sauropod-inhabited ecosystems, some of which, including the Morrison, have been interpreted as arid and highly water-stressed environments; however, the water-stressed nature of the Morrison has been heavily criticized in several more recent works on the basis of fossil evidence for the presence of extensive forest cover and aquatic ecosystems.

[29] However, there is actually little evidence of gregarious behavior in theropods,[53] and social interactions with members of the same species would have included antagonistic encounters, as shown by injuries to gastralia[33] and bite wounds to skulls (the pathologic lower jaw named Labrosaurus ferox is one such possible example).

Dinosaurs known from the Morrison include the theropods Ceratosaurus, Ornitholestes, Tanycolagreus, and Torvosaurus, the sauropods Haplocanthosaurus, Camarasaurus, Cathetosaurus, Brachiosaurus, Suuwassea, Apatosaurus, Brontosaurus, Barosaurus, Diplodocus, Supersaurus, Amphicoelias, and Maraapunisaurus, and the ornithischians Camptosaurus, Dryosaurus, and Stegosaurus.

Many of the dinosaurs of the Morrison Formation are the same genera as those seen in Portuguese rocks (mainly Allosaurus, Ceratosaurus, Torvosaurus, and Stegosaurus), or have a close counterpart (Brachiosaurus and Lusotitan, Camptosaurus and Draconyx).

[174] A bone assemblage in the Upper Jurassic Mygatt-Moore Quarry preserves an unusually high occurrence of theropod bite marks, most of which can be attributed to Allosaurus and Ceratosaurus, while others could have been made by Torvosaurus given the size of the striations.